1. Field of the Invention
The present invention relates to a manufacturing method of an anti-corrosive multi-layered structure material having an anti-corrosive non-metallic surface layer formed on a metallic substrate layer.
2. Discussion of the Prior Art
An anti-corrosive multi-layered structure material having an anti-corrosive non-metallic surface layer formed on a metallic substrate layer can be manufactured in the form of a light weight material at a low cost in comparison with an anti-corrosive metallic material made of a high-nickel chromium alloy. The multi-layered structure material is used as a material of various kinds of structures in a corrosive atmosphere.
In the anti-corrosive multi-layered structure material, an inexpensive metallic material inferior in anti-corrosiveness is used as a material of the metallic substrate layer, and various kinds of fine ceramic powder or fine carbon powder is used as a component material of the non-metallic surface layer. The fine ceramic powder or fine carbon powder is layered on the metallic substrate layer by coating, sputtering or electrophoresis method. As a result, numberless fine pores are formed in the non-metallic surface layer of the structure material and opened into the non-metallic surface layer from the surface of the metallic substrate layer. Accordingly, in use of the anti-corrosive multi-layered structure material in a corrosive atmosphere, the metallic substrate layer is corroded due to corrosive liquid or gas invaded into the fine pores in the corrosive atmosphere, and the non-metallic surface layer is peeled off from the surface of the metallic substrate layer.
To ensure anti-corrosiveness of the multi-layered structure material, it is required to fill up the numberless pores inevitably formed in the non-metallic surface layer during the manufacturing process. In Japanese Patent Laid-open Publication No. 4-187779, there is disclosed a treatment method of filling up the numberless pores in the non-metallic surface layer by non-electrolytic plating of anti-corrosive metal. Disclosed also in Japanese Patent Laid-open Publication No. 6-228762 is a treatment method of filling up the numberless pores in a non-metallic surface layer of another type by non-electrolytic plating of gold superior in anti-corrosiveness.
As in the treatment methods disclosed in the publications, selection of the metal used for non-electrolytic plating depends only on control of a temperature, it is difficult to plate only the interior of pores with the selected metal without plating useless portions of the surface of the multi-layered structure material. Since the anti-corrosive metal such as gold used for non-electrolytic plating is expensive in comparison with the metal used for the metallic substrate layer, the treatment cost of the surface of the multi-layered structure material increases.
In the treatment method disclosed in the Japanese Patent Laid-open Publication No. 6-228762, the non-electrolytic plating of gold is carried out on the entire surface of an intermediate layer in the form of a special metal plated skin membrane or a strike skin membrane formed on the surface of the metallic substrate layer. This results in extreme increase of the treatment cost of the surface of the multi-layered structure material.
It is, therefore, a primary object of the present invention to provide a manufacturing method of an anti-corrosive multi-layered structure material capable of filling up only fine pores in a non-metallic surface layer formed on a metallic substrate layer at a low cost.
According to the present invention, the object is attained by providing a manufacturing method of an anti-corrosive multi-layered structure material having an anti-corrosive non-metallic surface layer formed on a metallic substrate layer, wherein non-electrolytic plating of an anti-corrosive metal different in ionization property from the surface metal of the metallic substrate layer is carried out on the surface of the non-metallic surface layer so that the anti-corrosive metal is substituted for the surface metal of the metallic substrate layer through fine pores of the non-metallic surface layer and precipitated only in the fine pores of the non-metallic surface layer without causing any precipitation of the anti-corrosive metal on a useless portion of the non-metallic surface layer.
According to an aspect of the present invention, there is provided a manufacturing method of the anti-corrosive multi-layered structure material, wherein non-electrolytic plating of an anti-corrosive metal catalytic with the surface metal of the metallic substrate layer is carried out on the surface of the non-metallic surface layer so that the anti-corrosive metal catalyzes with the surface metal of the metallic substrate layer through fine pores of the non-metallic surface layer and precipitated only in the fine pores of the non-metallic surface layer without causing any precipitation of the anti-corrosive metal on a useless portion of the non-metallic surface layer.
In the manufacturing methods described above, the non-metallic surface layer is provided in the form of a carbon layer or a conductive ceramic layer, and the anti-corrosive multi-layered structure material can be used as a separator in a fuel cell. In a practical embodiment of the present invention, the non-metallic surface layer may be provided in the form of a carbon layer or a conductive ceramic layer of TiN or TiC to provide a light weight separator superior in anti-corrosiveness for use in a fuel cell. In the case that the non-metallic surface layer is provided in the form of a carbon layer, the surface treatment of the metallic substrate layer can be carried out at a low cost. Accordingly, the anti-corrosive multi-layered structure material can be provided as a useful material for a separator used in a corrosive environment of a fuel cell.
In the case that the anti-corrosive multi-layered structure material is used in a high temperature corrosive atmosphere, it is desirable to provide a non-metallic surface layer made of heat resistant ceramic such as SiO2, Al2O3 or the like. In the case that the anti-corrosive multi-layered structure material is used in a low temperature corrosive atmosphere, it is desirable to provide a non-metallic surface layer made of anti-corrosive synthetic resin such as polyethylene, polypropylene, terafluoroethylene or the like.